Liquid entrainment is a problem frequently encountered in distillation tray technology. Gas-liquid contacting employing plate and tray columns and potential problems involved are discussed in Section 18 of The Chemical Engineers' Handbook, Fifth Edition, by Robert H. Perry and Cecil H. Chilton. Tray designs with baffles and dispersers of various types are illustrated and discussed.
Copending application Ser. No. 08/833,490 (which is commonly owned with the instant invention)is directed to a means of de-entraining liquid. In Ser. No. 08/833,490, a plurality of de-entrainment devices (such as vane packs) on the trays are specified to accomplish the vapor/liquid de-entrainment.
A series of conventional sieve trays is illustrated in FIG. 1. Liquid that is entrained upwards from the tray can be thrown up against the perforated area of the tray above, and get carried up to the next tray. This backmixing of liquid up the column, contrary to the desired downward liquid flow, can greatly decrease the separation efficiency of the column and can cause flooding (hydraulic overloading) of the column.
U.S. Pat. No. 4,356,132 (Belyakov et al) discloses a mass-transfer apparatus which comprises a vertical cylindrical housing, contact trays accomodated inside the housing and made up of perforated and non-perforated sectors, the neighboring trays being arranged so that the perforated sectors of one tray overlie the non-perforated sectors of another tray and vice-versa. The overflow passageways of the contact trays are positioned on the non-perforated sectors. Overflow deflectors are arranged on the contact trays, and baffles are adapted to extend downwardly from each contact tray from the borderline between the perforated and non-perforated sectors and inclined toward the perforated sector. Belyakov differs from the instant invention in that it does not teach the use of multiple baffles vertically located between the perforated area and the impermeable roof, in order to decrease entrainment of liquid. The instant invention imparts co-current flow of both gas and liquid with substantially all the liquid being purposely entrained upward into the vanes (or baffles) where the liquid is deflected downward, at an angle, into a disengaging area opposite the perforated area where the liquid and gas efficiently separate. Belyakov's device specifically does not act in this way as illustrated by Belyakov's Figure's 3 and 6 (see solid and dashed flow lines). Our invention has a rather large sloping open disengaging area extending well below the plane of and opposite the perforated area for enhanced separation of liquid from vapor. Belyakov has no such area extending below the plane of the perforated area.